1. Field of the Invention
This invention relates to lubricating oil compositions, particularly to lubricating oil compositions useful as functional fluids in systems requiring coupling, hydraulic fluids and/or lubrication of relatively moving parts. It is concerned with functional fluids for use in the lubrication of heavy machinery, particularly high-power-output tractors. More particularly, the present invention is concerned with the reduction of brake and clutch noise.
2. Description of the Related Art
The use of heavy machinery, such as a tractor, has increased the demand for high-performance lubricating compositions. Modern tractors have many power-assisted components, such as power steering and power brakes. Power brakes can either be of the drum-type or disc-type. The disc-type brakes are preferred, since they have greater braking capacity than drum-type brakes. The preferred disc brakes are the wet-type or oil-immersed brakes, which are immersed in a lubricant and are therefore isolated from dirt and grime. The wet-type brakes are in contact with the lubricating oil.
Such brakes suffer from at least one problem, namely, brake chatter or brake squawk. Brake chatter is a phenomenon where the torque variation of the friction material or reaction plate is large, so as to create harmonic vibrations in the equipment. These vibrations convert to objectionable sound. This phenomenon is a very unpleasant noise that occurs upon application of the brake.
Generally, additives formulated for lubricating oil compositions where the fluid will contact brake materials contain friction modifiers to control brake chatter. The use of friction modifiers of the proper kind reduces the amplitude of the torque variation and reduces the sound. In the past, friction-modifying agents, such as dioleylhydrogen phosphite, have been added to the lubricating oil composition to reduce the brake chatter. Controlling the brake chatter may have the negative side effect of lowering the brake capacity, making the equipment harder to bring to stop.
A further complication in eliminating brake chatter is the desire to use the same functional fluid, not only for the brake lubrication, but also for lubrication of other tractor parts, such as the hydraulic and mechanical power take-offs, the tractor transmission, gears and bearings, and the like. Gear wear may be improved by one friction modifier and not another. Lubricating compositions containing dioleylhydrogen phosphite tend to suffer from very high wear rates, particularly at high temperature. The functional fluid must act as a lubricant, a power transfer means, and as a heat transfer medium. Obtaining a compounded fluid to meet all of these needs without brake chatter is difficult.
It has now been discovered that a certain combination of one or more oil-soluble fatty acid esters of a polyhydric alcohol and one or more oil-soluble fatty acid amides act as appropriate friction-modifying agents, which when added to a lubricating oil, exhibit good anti-chatter characteristics and gear wear.
Accordingly, the present invention provides an additive composition comprising at least one mixture of additive components comprising:
a) from about 0.5 to about 20 wt % of one or more oil-soluble fatty acid esters of a polyhydric alcohol, and
b) from about 0.5 to about 20 wt % of an oil soluble fatty acid amide.
Another aspect of the present invention provides a lubricating oil composition comprising:
a) a major amount of at least one base oil of lubricating viscosity, and
b) at least one mixture of additive components comprising:
(i) from about 0.05 to about 2.0 wt % of one or more oil-soluble fatty acid esters of a polyhydric alcohol, and
(ii) from about 0.05 to about 2.0 wt % of one or more oil-soluble fatty acid amides.
A further aspect of the present invention provides for an additive concentrate containing one or more diluents and one or more of the additive compositions of the present invention.
A further aspect of the present invention provides a method for making an additive composition and a lubricating oil composition of the present invention by blending the components of the present invention. The resulting respective compositions may contain mixtures of components.
A still further aspect of the present invention also provides a method of lubricating friction material interfaces with a lubricating oil composition of the present invention.
Finally, the present invention provides a method of reducing brake chatter by lubricating the contacting surfaces of brakes with a lubricating oil composition of the present invention.
Among other factors, the present invention is based on the surprising discovery that the unique combination of one or more oil-soluble fatty acid esters of a polyhydric alcohol and one or more of the oil-soluble fatty acid amides in at least one base oil of lubricating viscosity, significantly reduces brake chatter in oil-immersed disc brakes of heavy duty machinery, such as tractors and still provides good gear wear protection.